Constructing buildings responsibly takes proper planning and awareness of the total environmental impact. The builder, after receiving a set of solar home building plans, begins the construction process.
Construction factors to consider
- Project planning / sequence of events
- Low impact site work
- Job site organization / material recycling
- Material source and delivery
- Construction process / advanced framing technique
- Sub-contractors / communication
- Waste management
The thermal envelope or ‘shell’ of a building is the framework with all exterior surfaces that come in direct contact with the outside air and environment. In a cold climate like New England, the shell must be very well insulated to prevent heat loss during the winter, and at times, heat gain during the summer. One of the main requirements of a passive solar home is a very well-insulated shell in order to retain warm indoor air and prevent heat loss.
Considerations for the thermal envelope:
- Insulation / heat loss / thermal conductivity
- Air infiltration / moisture control
- Window / door performance
In order to build a more energy efficient building, the exterior ‘shell’ has to be designed to reduce heat loss by reducing thermal conduction and bridging by increasing the insulated area. If the structural framework of a building can be reduced by using less wood, and that same area is replaced by insulation, then the assembly will be more energy efficient and in some cases use less material. Framework can also be arranged and divided to create a thermal break, adding further efficiency and reducing thermal bridging.
- Floors assembly
- Walls assembly
- Roof assembly
Concrete has a high embodied energy factor. Keeping the foundation layout simple and as small as possible is an obvious strategy towards green construction. There are two common foundation designs used in conjunction with small affordable homes:
Slab on grade – uses a standard 8” frost wall at the perimeter that is modified using xps to contain and isolate a 4”concrete slab, which has a minimum of 6” eps with 10mm vapor barrier.
Crawl space –this method uses a standard 8” frost wall at the perimeter with the understanding that a super insulated wood floor assembly will be build on the foundation. This method requires the use of a continuous vapor barrier and natural cross ventilation, producing an unconditioned space.
In both cases all utilities are located within the thermal envelope. Full foundations are avoided whenever possible due to the increased cost, thermal and moisture control. In the event a full basement is required, insulated concrete forms (icf) are often used.
There are two insulation camps: the natural fibre and cellulose camp vs. foam. We at Maine Sunworks are committed to and believe in the performance, low environmental impact and health associated with using cellulose, both loose and dense pack, mineral wool batt, and mineral wool board.
Foam – the properties of various foam products such as xps, eps absolutely have a place in modern building construction, particularly when in direct contact with earth, wet or moist areas. Foam is appropriate for all below-grade work with concrete foundations and under slabs.
We believe that the entire thermal envelope above grade should be insulated using cellulose and/or mineral wool, and there is no need to have foam above grade. The one exception is during air sealing a shell around windows and doors. The use of direct petroleum-based products should be limited in the construction of a ‘green’ home.